Streptococcus mutans is a universal colonizer of the human oral cavity and is considered a primary causative agent of dental caries. The organism has evolved to utilize a wide variety sugars and macromolecules in order to generate energy which allows it to adapt to numerous environmental conditions. A common environmental condition encountered by S. mutans is near or complete anaerobiosis: life with little or no oxygen. This condition is often found in the oral cavity within complex, multi-species biofilms where nutrients are scarce and competition between species is fierce. One important molecule that must be successfully gleaned is riboflavin, an essential vitamin critical for co-factor generation as well as the activation of pyruvate formate lyase (PFL) by the PFL activating enzyme (PFL-AE). Recent work has indicated that the primary mechanism for S. mutans riboflavin acquisition lies proximal to a putative PFL-AE, which also is in close neighborhood association with genes encoding the CidAB proteins. Expression of cidAB is highly upregulated during anaerobic growth, under transcriptional control of CcpA, and this operon is important for S. mutans oxidative stress resistance. Furthermore, the LrgAB proteins (homologous to CidAB) have been shown to act as pyruvate transporters in Bacillus subtilis. Our collaborator's data indicates a similar role for LrgAB in S. mutans, and our lab's preliminary data suggests that CidAB functions in the transport and/or metabolism of formate in this organism. This data, combined with the predicted functions of genes within the chromosomal neighborhood of the cidAB operon, suggests an important role for this genomic region in anaerobic metabolism. This project seeks to better understand this aspect of S. mutans physiology by using a combination of genetic, metabolic, and proteomics approaches to interrogate a) how this organism obtains and metabolizes riboflavin during anaerobic growth using a novel molecular vitamin probe and b) how the CidAB proteins function in formate transport and/or metabolism by analyzing metabolite profiles and physiological changes during anaerobic growth. These objectives will advance our understanding as to how S. mutans is able to persist and compete within human oral cavity, and how the organism is able to adapt its complex metabolism to different environmental conditions. Furthermore, increased understanding of these processes will provide key insights into how S. mutans contributes to dental caries, as well as novel targets for anti-microbial therapeutics.